The invention concerns an open-end spinning device with two friction rollers driven in the same direction and forming a spinning nip, of which the friction roller rotating towards the spinning nip is a suction roller, whereby the fibers fed into the spinning nip are twisted together into a thread in a yarn-forming zone.
In such a spinning device the friction rollers are provided with sectors subjected to negative air pressure so that the fibers are caused to fly into the nip area (DE-PS-No. 24,49,583). It also suffices if only one of the friction rollers is subjected to negative air pressure (EP-OS No. 00,62,404). In order to facilitate the flight of the fibers these sectors are large, in relation to the friction rollers' periphery, and are located on the side of the spinning nip, in the peripheral sense. Because of the size of the suction sectors air consumption is high in these devices. It has furthermore been shown that in such spinning devices the quality of the yarn deteriorates considerably at high spinning speeds.
It is the objective of the present invention to avoid the disadvantages and to create a device making it possible to spin a yarn of good quality, even at high spinning speeds.
This objective is attained in a device according to the introductory clause of claim 1 of the invention by providing at least one sector subjected to negative air pressure in the range of the yarn forming zone, in the spinning nip, whereby the width of said sector extends, in the peripheral sense, from the yarn forming zone to beyond the plane connecting the axes of the friction rollers towards the side opposite to the spinning nip. It was also shown that such as arrangement or the suction zone has a very beneficial influence upon the imparting or torsion to the yarn.
The sector subjected to negative air pressure can be very narrow, with a width from 4 to 8 mm and preferrably 6 mm wide, so that air consumption is extremely low. The middle of the sector subjected to negative air pressure is located within the plane connecting the axes above the friction rollers or at a distance of the axes-connecting plane, in the peripheral sense, on the side opposite to the spinning nip. Thus a suction zone of sufficient size for the required air flow rate is obtained, yet a concentration upon the yarn forming zone is achieved. It has been shown that the imparting of torsion to the yarn is greatly enhanced with such a design, even at high spinning speeds. Conveying of the fibers is enhanced if a sector of lesser negative air pressure procedes the sector of great negative air pressure on the friction roller rotating towards the spinning nip. Best results from the point of view of yarn strength are obtained if the middle of the sector subjected to suction air is spaced extends 1 mm from the plane connecting the friction rollers, on the side opposite to the spinning nip.